The instant invention relates to the dry clean-up of gases in hot lime (CaO) wherein the lime (CaO) is regenerated and sulfur(S) is recovered in elemental form.
In particular this invention is an improvement over the process described on pages 94 and 95 of the 1981 Generation Planbook edition, entitled "Gasifier Produces Clean Fuel from Resid and Lignite for Natural-gas-fired Boiler", a copy of the article being attached for reference.
This reference describes the injection of a high-sulfur fuel such as oil or coal, into a hot bed of calcined limestone (CaO) which is contained in a first reactor, the calcined limestone (CaO) being fluidized by a mixture of flue-gas and air to gasify the oil or coal. When the calcined limestone (CaO) becomes spent and takes the form of calcium sulfide (CaS) it is physically transferred while hot to a second reactor for regeneration with air (O.sub.2) to convert the calcium sulfide (CaS) back to calcined limestone (CaO) and thereby yield a sulfur dioxide (SO.sub.2) off-gas. The hot regenerated calcined limestone (CaO) is then physically returned to the first reactor for further sulfur collection from the high-sulfur oil or coal. The sulfur dioxide (SO.sub.2) off-gas produced is directed from the second reactor to a third reactor where coal is charged to supply the carbon needed for forming elemental sulfur(S). Ash from the coal leaves as a residue from the third reactor.
The disadvantagees of the reference are as follows:
1. The fuel such as the oil or coal is gasified with the lime (CaO); this causes the creation of excessive fines and the mixing of the ash with the desulfurizing agent (CaO), which decreases the efficiency of sulfur(S) collection by the lime (CaO) thereby causing the increase of lime (CaO) consumption and a greater disposal problem.
2. The physical transfer of the hot spent lime in the form of calcium sulfide (CaS) to a second reactor for regeneration and the physical transfer of the hot regenerated lime (CaO) back to the reactor where the gasification takes place are movements which necessitate the moving of hot material which is erosive and abrasive resulting in the increase of maintenance costs and the creating of additional fines which must be disposed of.
3. The directing of the sulfur dioxide (SO.sub.2) to a third reactor where it mixes with coal for the formation of elemental sulfur(S), generates a tail gas which must be recycled, ash from the coal that must be disposed of, and the reaction of coal with sulfur dioxide (SO.sub.2) requires control air which must be fed to the third reactor.
4. The capital and operating costs are too high.